The present invention relates generally to wireless communications and more particularly to reducing data loss during cell handoffs.
Because users of cellular telephones often travel while carrying on communications sessions, cellular radio systems support handoffs of ongoing sessions between cells. This allows a cellular phone user to start a session in one cell and continue the same session while traveling through any number of other cells. During transitions between cells, some of the information associated with a communications session may be lost. Because cellular systems handle primarily voice communications, these small gaps of information have not been perceived as a significant problem, since small losses may be imperceptible to the participants in a voice communications session. However, in data communications, small losses of information during transitions between cells may adversely impact data communications and reduce data throughput. Moreover, in an attempt to increase data throughput for data communications sessions, some wireless communication protocols sacrifice some of the control channels to make room for session data. However, this decrease in control aggravates problems of data loss associated with transitioning between cells.
In accordance with the present invention, techniques for reducing data loss during handoffs are provided which substantially eliminate or reduce disadvantages and problems associated with previous techniques. In a particular embodiment, the present invention satisfies a need for a communications control technique that, upon detecting an imminent handoff, reduces the window size of transmissions to reduce or eliminate packet loss during the handoff.
According to one embodiment of the present invention, a method for reducing data loss in wireless communications communicates data associated with a communications session between a mobile unit and a first base station. The method communicates the data using first transmission parameters that include a first window size. The method determines an imminent transmission of the communications session from the first base station to a second base station and, in response to determining the imminent transition, communicates data between the mobile unit and the first base station using second transmission parameters. The second transmission parameters include a second window size smaller than the first window size to reduce data loss during the transition from the first base station to the second base station.
In accordance with another embodiment of the present invention, a mobile unit includes an interface that transmits data associated with a communications session. The interface transmits the data using first transmission parameters that include a first window size. The mobile unit also includes a controller that determines an imminent transmission of the communications session from the first base station to a second base station and, in response to determining the imminent transmission, requests second transmission parameters for transmissions to the first base station. The second transmission parameters include a second window size smaller than the first window size to reduce data loss during the transition from the first base station to the second base station.
The invention provides a number of technical advantages. Using these techniques, communications systems can reduce or eliminate packet loss during handoffs. By modifying transmission parameters, such as a window size and code book, systems may limit the amount of data that can be lost during a handoff. For example, by reducing a transmission window size before a handoff between base transceiver stations, the system reduces the maximum number of packets that can be lost before the loss is detected. Therefore, the system can reduce or eliminate communications delays resulting from detection and retransmission of packets lost during handoffs.
Reducing packet loss during handoffs also provides other advantages. For example, reducing losses due to an unreliable medium (wireless communications) prevents packet communications protocols from interpreting those losses as congestion. That is, some protocols, such as transmission control protocol (TCP), are based on an assumption that the underlying media for communications are relatively reliable. Therefore, in these protocols, packet losses are attributed to congestion, which may cause these protocols to reduce throughput. In addition, reducing packet loss during handoffs allows wireless communications systems to more readily facilitate xe2x80x9cconnectionlessxe2x80x9d services, such as user datagram protocol (UDP) that rely on an underlying reliability of the media used for communications.